Control system.



R. E. HELLMUND.

CONTROL svsrsm.

v APPLICATION FILED FEB-3.1915. I

Patented Mar. 5, 1918.

INVENTOR Rudolf E, Hellmund.

{ATTORNEY go og v z llllllllll lll'll f 4 E88 single-phase source of energy amin UNITED. STATES PATENT OFFICE.

BUDOIJ' I. OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB TO WESTING- HOUSE ELECTRIC AND KANUIACTUBING COMPANY, A CORPORATION 01" PENNSYL- OON'I'BOL SYSTEM.

VANIA.

To all whom it may concern:

a subject of the German Empire, and a resident of Pittsburgh in the county of Allegheny and State 0 Pennsylvania, have invented a new and useful Improvement in Control Systems, of which the following is as ecification.

y invention relates to control systems for alternating-current dynamo-electric machines, and it has special reference to the control and regulation of polyph'ase railway induction motors that are operated from a through the agency of a phase converter.

One of the objects of my invention is to provide a simple s stem of the above-indicated class which s all be. effective and reliable in operation and which shall be particularl adapted to compensate for inherent phase istortions and voltage reductions in the phase converter under load conditions, and, moreover, to maintain balanced phase relations and full voltage as well as ood power-factor upon the motor under oad conditions. I

In a co-pending application, Serial No. 808,714 filed December 26, 1913, by Ben- Lamme and assigned to the Westmghouse Electric & Manufacturing Company, a system of this general type is disclosed in which the converter phase distortions and voltage reductions are compensated for by suitable adjustments of the phase-converter connections with respect to the transformer which serves to supply single-phase energy thereto.

According to my present invention, I propose to insure balanced phase relations and normal magnitude of the volta e supplied to the driving motor by means 0 an lnductive reactance connected 1n series circuit with one of the motor phase windin for the purpose of correcting for the placement of phase and also by means of a switching device for varying the taps of the transformer, whereby the voltages may be increased to any desired amount. By mason of the fact that the introduction of the inductive react ance tends to lower the ower-factor of the driving motor, it is desirable to employ a phase advancer of any well-known form for maintaining the power-factor at a proper value, under load conditions.

Specification of letters Patent.

Application ma I'ebruary a, mu. Serial No. am.

In the accompanying drawing, Figure 1 is a diagrammatic view of a system of control embodying my invention, and Fig. 2 is a vector diagram showing the relationships of certain of the voltages of the system shown in Fig. 1. Y

Referrin to the drawing, a supply conductor 1, wiich may conveniently constitute a, trolley conductor of an electric railway system, delivers single-phase energy to a primarywinding 2 of a transformer 3 havmg a secondary winding 4. The primary winding 2 is provided with a plurality of end taps 2 which are adapted to be connected to the ground G through a switching device 5, whereby the ratio of transformation between the primary and secondary winding ma be varied at-will.

Connecte to the secondary winding 4 of the transformer 3 is a polyphase induction motor 6 that is adapted to receive energy therefrom through a phase converter 7 that is interposed between the transformer windingr4 and said motor.

he motor 6 is of the three-phase starconnected wound-rotor type, havin a plurality of primary windings 9, 10 an 11 and a plurality of secondary windings 12, 13 and 14. The outer terminals of the secondary windin 12,- 13 and 14 are connected to an adjusta 1e resistance device, such as a liquid rheostat 15, while the inner terminals thereof are connected together, at the star int, through an armature 16 of an auxiliary Patented Mar. 5, 1918.

hase advancer '17 which performs its usual 'unction of maintainin a good power-factor in accordance with wel -known principles.

The phase advancer 17 pertains only indirectly to my present invention and, althou h prefer to employ an advancer of the we known Le Blane type that is provided with a field-ma et structure without windings,

any suitab e form of apparatus for accomplishin the desired result may be used.

For riving the phase advancer 17 I have shown an auxiliary motor DM of the threephase, wound-secondary type, which is driven from the primary circuit of the main motor 6, and is rovided with a secondarycircuit variable t rec-phase resistor R. Ap-

ropriate adjustments of the resistor R may be made in any well-known manner, as by a switching device SD, to perform desired phase-regulating functions. It will be understood that any other suitable driving, 6

. the secondary winding 22 has one of its terminals wnnected substantially to the midpoint of the transformer winding 4 and is designed to deliver a uadrature voltage of substantially 86.6% 0 that of the transformer winding 4%. Moreover, the converter winding 22 is connected in series with the primary windin conductor 24, while the motor windings 10.

and- 11 are connected in multiple with the; transformer winding 4 through conductors 25 nd 26, respectively.

I"); the purpose of compensating for the inherent phase distortion of the converter 7 under load conditions and for maintaining balanced phase relations of the voltage supplied to the motor 6, an inductive re-. actance device27 is connectedin conductor 25 in series circuit with the motor phase winding 10.

With the circuit connections as shown and the motor 6, operating at light or re load, balanced polyphase voltages are supplied thereto, as will be readily understood by those skilled in the art and as clearly indi- 'cated in Fig. 2 to which reference may now be made.

In the figure, a-b represents the voltage of the transformer winding 4, while c represents that of the converter secon ary winding 22 which is of such value and phase position as to combine with the voltage a-b to produce balanced three-phase voltages a-b, 6-0 and ca-, which voltages are supplied to the driving motor 6 under the conditions assumed.

If, however, the motor 6 is loaded, there results an inherent displacement of the phase position of the converter voltage which causes the point 0 to occupy a position 0'. Were it not for the inductive reactanoe device 27 therefore, the voltages supplied to the motor 6 would be unbalanced and represented by the triangle 060. However, by-

employing the inductive reactance 27 and properly choosing its value with respect to the normal load conditions, a. voltage drop is produced therein represented by the line azl which serves to maintain balanced phase relations and voltages upon the motor 6, as represented by the triangle dba'. This condition of balanced voltages depends, of course, upon the proper choice of inductance to meet the normal service condi- 9 of the motor 6 through .reactive drop produced tions, and it will be noted that, while the voltages are balanced with respect to phase positions, the magnitudes thereof are somewhat reduced from that initially supplied to the motor.

Full volta es, however, ma be obtained readily by s ifting the switc ing device 5 to the proper inner tap2, whereby an increased voltage is delivered to the trans former secondary winding 4 and, consequently, to the converter windin 22. Therefore, the resultant polyphase vo tages are also correspondingly increased, and, balanced voltages of full normal value are thus supplied to the driving motor 6.

The effect of the inductive reactancc 27 is to lower the power-factor of the driving motor, which, however, may be im roved or, in fact, maintained at an desire value by suitable adjustments of t e phase advancer 17, as will be understood.

Qbviously, the advantages and benefits of my invention maybe obtained by means of apparatus and circuit connections which differ materially from those herein set forth but which embed the basic principles of my invention. I, t erefore, desire that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. In a converting system, the combination with a source of singlephase alternating current, of a pol phase load circuit, connections for trans erring ener directly from said source to one phase 0 said load circuit, a phase-converter, connections for combinin the tertiary electromotive force of said p ase-converter with the electromotive force of said source for energizing the remaining phases of said load circuit, and means for producin a reactive drop in said first named connections roportional to the y said phase-converter in said last-named connections, whereby the electromotive forces supplied to said load circuit may be maintained in substantial balance throughout wide load changes.

2. In a converting stem, the combination with a source of single-phase alternat ing current, of a polfyphase load circuit, connections for trans erring ener directly from said source to one phase 0 said load circuit, a phase-converter, connections for combinin the tertiary electromotive force of said p ase-converter. with'the electromothe force of said source for energizing the remaining phases of said load circuit, and a reactive element in said first-named connections designed to produce a reactive drop therein proportional to the reactive dro produced by said phase-converter in said last-named connections, whereby the electromotive forces supplied to said load circuit may be maintained in substantial balance throughout wide load changes.

' ing current, of a polfvphase load circuit, con- 7 means for compensatin nections fortrans erring ener directly from said source to one phase 0 said load circuit, a phase-converter, connections for combinin the tertiary electromotive force of said p ase-converter with the electrometive force of said source for energizing the remaining phases of said load circuit, means for produclng a reactive drop in said firstnamed connections proportional to the reactive drop produced by said phaseconverter in said last-named connections, whereby the electromotive forces supplied to said load circuit may be maintained in substantial balance throughout wide load changes, and

for the power-factor-diminishing effect 0 said reactive-dropproducing devices.

a converting system, the combination with a source of slngle-phase alternating current, of a pol phase load circuit, connections for transfirring ener directly from said source to one phase ci f said load circuit, a phase-converter, connections for combinin the tertiary electromotive force of said p ase-converter with the electromotive force of said source for energizing the remaining phases of said load circuit, a reactive element in'said first-named connections designed to produce a reactive drop therein proportional to the reactive dro produced by said phase-converter in sai last-named connections, whereby the electromotive forces supplied to said load circuit may be maintained in substantial balance throughout wide load changes, and a haseadvancing dynamo-electric machine e ectrically associated with said load circuit and adapted to compensate for the power-factorreducing effects of said reactive elements.

5. The combination with a source of single-phase energy, a transformer connected thereto, a three-phase inducticn motor, and

a phase converter interposed between said motor and said transformer and having an exciting winding connected across said transformer and a secondary winding connected to the midpoint of said transformer, of an inductive device in series circuit with one phase of said motor for compensating for phase distortions in said converter under load conditions, and means associated with said transformer for varying the polyphase voltages supplied to said motor.

6. The combination with a'source of single-phase energy, a transformer connected thereto, a three-phase induction motor having a star-connected secondary winding and a phase converter interposed between said transformer and said three-phase motor for supplying three-phase energy to said motor, of an inductance connected in series with one of the phases of said motor for maintaining balanced phase relations under load conditions, means associated with said transformer for increasing the magnitude of the polyphase voltages supplied to said motor under load conditions, and a base advancer connected in the star-point of the motor secondary windings for regulating the powerfactor of the motor under load conditions.

In testimony whereof, Ihave hereunto subscribed my name this 30th day of Jan. 

